Fitting structure of automatic transmission

ABSTRACT

A fitting structure of an automatic transmission is comprised of a fitting member which is cylindrical, and a receiving member which is comprised of an opening portion to be fit with the fitting member. A diameter of a lead end of the fitting member is larger than a diameter of a rear end thereof, and a difference between the diameters of the lead end and the rear end are within elastic deformation range of the receiving member. A tightening force is created after fitting for holding the fitting member securely. An entire circumference of an edge portion of the lead end of the fitting member is formed with a predetermined curvature.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a fitting structure of an automatic transmission, in particular, it relates to a fitting structure of an oil pump cover and a stator shaft.

[0002] Japanese Patent Provisional Publication (Heisei) 11-294555 discloses a fitting structure of an automatic transmission. This fitting structure is for use when press-fitting a stator shaft into an inner circumference of an oil pump cover. The stator shaft comprises serrated large-diameter portion for serration-fitting with the oil pump cover, and a small-diameter portion for press-fitting with the oil pump cover.

SUMMARY OF THE INVENTION

[0003] However, although superior fitting force can be achieved to counter torque acting circumferentially about the axis with the above related art, there is still the problem with ample fitting force not being achieved to counter torque acting in the axial direction.

[0004] In the related art, a stator shaft passes through an oil pump cover, a one-way clutch of a torque converter being fixedly supported at one end thereof, and a drum or similar rotating body being revolvingly supported at another end thereof. In an instance where a torque converter comprises a lockup clutch, a lockup piston slides axially accompanying engagement and disengagement of the lockup clutch. Thrust force due to this axial sliding is input into the one-way clutch via thrust bearings and other elements, and also adversely acts on the stator shaft axially. As the oil pump cover is fixed to the transmission case, there may also be a lack of fitting force to firmly hold the stator shaft. This would allow undesirable vibratory motion when torque acts axially in both the direction in which the stator shaft has been press-fit and the opposite direction.

[0005] Also, a plurality of hydraulic passages are disposed in the oil pump cover for supplying hydraulic pressure from a control valve unit to various elements including individual friction elements, and supply hydraulic pressure via hydraulic passages within the stator shaft to other areas including passages within various shafts. Here, if positioning of the oil pump cover and the stator shaft fall out of alignment due to vibratory motion, it is possible for line resistance to become unfavorably large, leading to a degrade in ability to control hydraulic pressure.

[0006] It is therefore an object of the present invention to provide a fitting structure of an automatic transmission, which is capable of securely holding a stator shaft without the occurrence of vibratory motion, not only with respect to torque acting circumferentially about the shaft but also with respect to torque which is input and acting in the axial direction.

[0007] An aspect of the present invention resides in a fitting structure of an automatic transmission, the fitting structure comprising a fitting member which is cylindrical, a diameter of a lead end thereof being larger than a diameter of a rear end thereof, and a receiving member comprising an opening portion to be fit with the fitting member, the receiving member being formed from a material of less rigidity than the fitting member.

[0008] Another aspect of the present invention resides in a fitting structure of an automatic transmission, the fitting structure comprising a fitting member comprising a fitting portion which is cylindrical, the fitting portion being formed in a tapering shape and a receiving member comprising an opening portion to be fit with the fitting portion, the receiving member being formed from a material of less rigidity than the fitting member.

[0009] A further aspect of the present invention resides in an assembly of an automatic transmission, the assembly comprising a fitting member comprising a fitting portion which is cylindrical, and a receiving member comprising an opening portion into which the fitting portion is fit, being formed from a material of greater elastic deformation than the fitting member, wherein a diameter of a lead end of the fitting portion being greater than a diameter of a rear end of the fitting portion, a difference between the diameters being within an elastic deformation range of the receiving member, a diameter of the opening portion of the receiving member being smaller than a diameter of the fitting portion, a tightening force being created in the receiving member by elastic deformation thereof after fitting of the fitting member into the receiving member for holding the fitting member, and an edge portion of the lead end of the fitting portion being formed with a predetermined curvature.

[0010] The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a cross sectional view showing an automatic transmission comprising a fitting structure according to an embodiment of the present invention.

[0012]FIG. 2 is an enlarged cross sectional view showing an oil pump cover and a stator shaft of the automatic transmission in FIG. 1.

[0013]FIG. 3A is an enlarged cross sectional view of the fitting structure in FIG. 2.

[0014]FIG. 3B is an enlarged cross sectional view showing the fitting structure in FIG. 3A after press-fitting.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Referring to FIGS. 1 through 3B, there is discussed an embodiment of a fitting structure of an automatic transmission in accordance with the present invention.

[0016] An oil pump B is disposed between a torque converter A and a transmission apparatus C as shown in FIG. 1. An impeller 21 of torque converter A and an oil pump drive shaft 2 of transmission apparatus C revolve together with an engine output shaft. Oil pump B comprises an inner gear 9 which is joined with oil pump drive shaft 2.

[0017] A body of oil pump B is constructed with an oil pump housing 3, an oil pump cover 4, and a stator shaft 7. Oil pump cover 4 is fixed to a transmission case 18 by bolts, and oil pump housing 3 and oil pump cover 4 are fixed by clamp bolts 5. Within oil pump cover 4, outer gear 8 is disposed on an outer circumference of inner gear 9. An oil seal 6 and a bushing 10 are disposed between oil pump housing 3 and oil pump drive shaft 2. Oil pump cover 4 and stator shaft 7 are fitted together through serration fitting and press-fitting.

[0018] Passages including an intermediate passage 7 a are disposed within oil pump cover 4 and stator shaft 7 for supplying hydraulic control pressure from a control valve unit (not shown) to each hydraulic passage including a torque converter pressure supply passage 12, a torque converter pressure drain passage 13, and lockup clutch pressure supply passage 14.

[0019] Torque converter A comprises impeller 21 which is coupled directly to an engine (not shown), a turbine 22, a stator 23, and a lockup clutch 26 which directly connects the engine and a shaft 11. Stator 23 is fixedly supported by stator shaft 7 through one-way clutch 24. Thrust bearings 24 a and 24 b are disposed at both sides axially of one-way clutch 24 so that a turbine hub 25 and oil pump drive shaft 2 are rotatably supported with respect to one-way clutch 24.

[0020] The left end of shaft 11 shown in FIG. 1 is splined, and is inserted into turbine hub 25 which supports lockup clutch 26 and turbine 22 of torque converter A. The state of connection between the engine and shaft 11 is controlled by a lockup piston 26 a of lockup clutch 26 axially sliding along an outer circumference of turbine hub 25.

[0021] Torque converter pressure drain passage 13 is disposed between shaft 11 and stator shaft 7. Hydraulic passages running within shafts such as lockup clutch pressure supply passage 14 are disposed in shaft 11, and supply hydraulic pressure from an intermediate passage 7 a to lockup clutch 26.

[0022] Stator shaft 7 is formed from a ferroalloy, and the shaft is designed to have a minimal of thickness while maintaining necessary strength to withstand torque input from one-way clutch 24 or a similar element, in order to strive for compactness of the entire structure. Referring to FIG. 2, stator shaft 7 comprises a shaft portion 70 which is of small diameter and fixedly supports one-way clutch 24 of torque converter A, a press-fitting portion 71 which is of mid-diameter and press-fits with oil pump cover 4, and a serration portion 72 which is of large diameter and serration-fits with oil pump cover 4. A stopper surface 73 is formed at the boundary of press-fitting portion 71 and serration portion 72 for prohibiting movement axially of stator shaft 7 toward torque converter A.

[0023] Oil pump cover 4 is formed from an aluminum alloy, to allow for a minimum of weight while maintaining necessary thickness. Oil pump cover 4 comprises a cover press-fitting portion 41 for press-fitting with press-fitting portion 71 of stator shaft 7, and a cover serration portion 42 for serration fitting with serration portion 72 of stator shaft 7. A cover stopper surface 43 is formed at the boundary of cover press-fitting portion 41 and cover serration portion 42 to abut with stopper surface 73 of stator shaft 7.

[0024] The process of press fitting oil pump cover 4 with stator shaft 7 will now be explained. As shown in FIG. 3A, press-fitting portion 71 comprises a lead end 71 a and a rear end 71 b, a diameter of lead end 71 a being larger than a diameter of rear end 71 b. A tapering surface is thereby formed on press-fitting portion 71, and has an angle θ. An inner diameter of cover fitting portion 41 of oil pump cover 4 is set smaller than an outer diameter of stator shaft 7 at lead end 71 a. This requires oil pump cover 4 to deform in order to press-fit oil pump cover 4 and stator shaft 7 together. Stator shaft 7, being made of a ferroalloy, is of a greater rigidity than oil pump cover 4, which is made of an aluminum alloy, thus oil pump cover 4 will deform to be press-fit with stator shaft 7. Further, a difference between the diameter of rear end 71 b and the diameter of lead end 71 a of press-fitting portion 71 is set to be within an elastic deformation range of oil pump cover 4, that is, oil pump cover 4 deforms during press fitting to fit over stator shaft 7 within a limit where oil pump cover 4 retains an elastic property.

[0025] As shown in FIG. 3A, press-fitting portion 71 comprises a lead edge 74, lead edge 74 being chamfered and having a predetermined radius of curvature R taken in a cross section axially of press-fitting portion 71. Lead edge 74 is chamfered about an entire circumference thereof. When stator shaft 7 is press-fitted into oil pump cover 4, first, press-fitting stress created by press-fitting oil pump cover 4 over lead edge 74 works in a direction to stretch cover press-fitting portion 41 diametrically and enlarge an inner-circumference thereof. Press-fitting is carried out in this manner while stretched oil pump cover 4 deforms within elastic deformation range.

[0026] Stress distribution after press-fitting can be seen from FIG. 3B. A fitting surface area indicated by the arrows is formed along the tapering surface of press-fitting portion 71 of stator shaft 7 by cover press-fitting portion 41 deforming within elastic deformation range. When a tightening force T created by the elastic deformation of cover press-fitting portion 41 acts on this fitting surface area, a force defined by Tcos θ acting in an inward diametrical direction and a force defined by Tsin θ acting in the axial direction toward torque converter A are created. Therefore, even if a load acts on stator shaft 7 in a direction to the right of FIG. 3B where stator shaft 7 would try to dislodge from oil pump cover 4, it is possible to gain a diametrical component of load as shown by the dotted lines extending diametrically from the arrows in the axial direction in FIG. 3B. Thus, it is possible to disperse a load which is opposite to the frictional force of the fitting surface generated by the tightening force due to the elastic deformation of oil pump cover 4, and it is possible to achieve an improvement of holding force for firmly holding a press-fitted member.

[0027] It is then possible to tighten the entirety of press-fitting portion 71 through elastic force by setting the diameter of the inner diameter of cover press-fitting portion 41 of oil pump cover 4 smaller than the diameter of stator shaft 7 at rear end 71 b.

[0028] The difference between the diameter of lead end 71 a and the diameter of rear end 71 b is set to be within the elastic deformation range of oil pump cover 4. Therefore, it is further possible to achieve an improvement in holding force while avoiding the problem of plastic deformation of oil pump cover 4, where elastic force would be lost and which would result in an inability to achieve ample tightening force.

[0029] As the entire circumference of edge portion of lead end 71 a of press-fitting portion 71 is chamfered and has a predetermined radius of curvature R taken in a cross section axially of press-fitting portion 71, it is easy for press-fitting stress to work in a direction to stretch cover press-fitting portion 41 of oil pump cover 4 in the diametrical direction during press fitting, making it possible to reduce load during press-fitting.

[0030] A plurality of hydraulic passages are disposed within oil pump cover 4, and enable supply of hydraulic pressure to passages within various shafts, for example, lockup clutch pressure supply passage 14 which is disposed in shaft 11. Thus, hydraulic passages of oil pump B are linked with lockup clutch pressure supply passage 14 via intermediate passage 7 a which is disposed in stator shaft 7. One-way clutch 24 is fixedly supported on stator shaft 7, and load acts axially accompanying engagement and disengagement of lockup clutch 26 via elements including thrust bearings 24 a and 24 b. If the portion where oil pump cover 4 and stator shaft 7 are in mutual fitting contact goes out of alignment due to this load, line resistance between hydraulic passages of oil pump B and hydraulic passages within the shafts becomes unfavorably large, inviting a possible degrading in ability to control hydraulic pressure. However, by applying the fitting structure of the present embodiment, it is possible to ensure proper fitting, and thereby prevent elements from falling out of alignment as well as prevent vibratory motion, arising from load acting in the axial direction. Therefore, degradation in the ability to control hydraulic pressure is eliminated.

[0031] This application is based on a prior Japanese Patent Application No. 2002-124729. The entire contents of a Japanese Patent Application No. 2002-124729 with a filing date of Apr. 25, 2002 are hereby incorporated by reference.

[0032] Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings.

[0033] For example, it is possible to achieve similar effects with the present embodiment applied to other fitting portions. Only the stator shaft was designed with a tapering surface in the first embodiment, however, it would also be possible to further increase fitting force by forming a tapering surface on the oil pump cover.

[0034] The scope of the invention is defined with reference to the following claims. 

What is claimed is:
 1. A fitting structure of an automatic transmission, the fitting structure comprising: a fitting member which is cylindrical, a diameter of a lead end thereof being larger than a diameter of a rear end thereof; and a receiving member comprising an opening portion to be fit with the fitting member, the receiving member being formed from a material of less rigidity than the fitting member.
 2. The fitting structure as claimed in claim 1, wherein the receiving member is elastically deformable within an elastic deformation range, a difference between the diameters of the lead end and the rear end of the fitting member being within the elastic deformation range.
 3. The fitting structure as claimed in claim 2, wherein a tightening force is created in the receiving member by the elastic deformation thereof after fitting the fitting member into the receiving member for holding the fitting member.
 4. The fitting structure as claimed in claim 1, wherein a diameter of the opening portion of the receiving member is smaller than a diameter of the fitting member.
 5. The fitting structure as claimed in claim 4, wherein an entire circumference of an edge portion of the lead end of the fitting member is chamfered.
 6. The fitting structure as claimed in claim 5, wherein the edge portion of the lead end of the fitting member has a predetermined curvature.
 7. The fitting structure as claimed in claim 1, wherein the fitting member is a stator shaft which rotatably supports an input shaft of the automatic transmission, and the receiving member is an oil pump cover disposed within the automatic transmission.
 8. The fitting structure as claimed in claim 7, wherein the stator shaft is made of a ferroalloy, and the oil pump cover is made of an aluminum alloy.
 9. A fitting structure of an automatic transmission, the fitting structure comprising: a fitting member comprising a fitting portion which is cylindrical, the fitting portion being formed in a tapering shape; and a receiving member comprising an opening portion to be fit with the fitting portion, the receiving member being formed from a material of less rigidity than the fitting member.
 10. The fitting structure as claimed in claim 9, wherein the fitting portion tapers inward from a lead end thereof to a rear end thereof.
 11. The fitting structure as claimed in claim 10, wherein a diameter of the opening portion of the receiving member is smaller than a diameter of the lead end of the fitting portion of the fitting member, a tightening force being created in the receiving member by the receiving member's being stretched after fitting to tighten the fitting portion about an entirety thereof.
 12. The fitting structure as claimed in claim 10, wherein an edge portion of the lead end of the fitting portion has a curvature about the entire circumference thereof defined by a predetermined radius of curvature taken in a cross section axially of the fitting portion.
 13. An assembly of an automatic transmission, the assembly comprising: a fitting member comprising a fitting portion which is cylindrical; and a receiving member comprising an opening portion into which the fitting portion is fit, being formed from a material of greater elastic deformation than the fitting member, wherein a diameter of a lead end of the fitting portion being greater than a diameter of a rear end of the fitting portion, a difference between the diameters being within an elastic deformation range of the receiving member, a diameter of the opening portion of the receiving member being smaller than a diameter of the fitting portion, a tightening force being created in the receiving member by elastic deformation thereof after fitting of the fitting member into the receiving member for holding the fitting member, and an edge portion of the lead end of the fitting portion being formed with a predetermined curvature. 